1. Field of the Invention
This invention relates to a thermally-responsive record material. It more particularly relates to such record material in the form of sheets coated with color-forming systems comprising chromogenic material (electron-donating dye precursors) and acidic color developer material. This invention particularly concerns a thermally-responsive record material capable of forming a substantially non-reversible image resistant to fade or erasure and useful for producing functional bar codes. The invention teaches an improved thermally-sensitive record material which when imaged with bar codes exhibit superior image properties cumulatively in terms of print contrast signal.
2. Description of the Related Art
Thermally-responsive record material systems are well known in the art and are described in many patents, for example. U.S. Pat. Nos. 3,539,375; 3,674,535; 3,746,675; 4,151,748; 4,181,771; 4,246,318; and 4,470,057 which are incorporated herein by reference. In these systems, basic colorless or lightly colored chromogenic material and acidic color developer material are contained in a coating on a substrate which, when heated to a suitable temperature, melts or softens to permit said materials to react, thereby producing a colored mark.
Thermally-responsive record materials have characteristic thermal response, desirably producing a colored image of sufficient intensity upon selective thermal exposure.
A drawback of thermally-responsive record material limiting utilization in certain environments and application has been the undesirable tendency of thermally-responsive record material upon forming an image to not retain that image in its original integrity over time when the thermally-responsive record material is handled or exposed to common liquids or oils or plasticizers such as found in skin oil, plastic food wrap, cooling oil and solvents such as common carbonless paper solvents.
Thermally-responsive record materials are increasingly utilized for bar code imaging, since such bar codes can be readily created by printer equipment in the field nearer the point of use and application.
Bar codes provide a convenient means for computerized inventory or goods handling and tracking. To function properly, it is necessary that the bar code have high print contrast signal, and that the thermally-responsive material on which the bar code is imaged resist unwanted bar width growth after imaging. The characters or bars must not only be intensely imaged, but must be sharp, and unbroken or free of pin holes. It is also necessary that when read by a scanner that a high percentage of scans result in successful decoding of the information in the bar code. The percentage of successful decodes of the bar code information must be maintained at a high value for the thermally-responsive record material to gain wide commercial acceptance for use in bar coding applications.
Print contrast signal relates to image intensity. Bar width growth relates to imaged bar dimensional stability and character sharpness. Percent decode relates to image integrity. Background contrast must also be maintained at a high level. Difficulties have been encountered attempting to bring together a confluence of these characteristics simultaneously in one coating formulation.
It is an object of the present invention to disclose an improved thermally-responsive record material having a high print contrast signal; high dimensional stability in terms of low bar width growth; a high percentage of successful decodes; and high contrast of the bar code with the background.